The mouse mshi mutation (for male sterility and histoincompatibility) defines a unique example of a minor histocompatibility (H) locus, one that may have resulted from mutation of a single, highly-conserved gene, and that appears to mediate an unusual allograft rejection mechanism that is independent of cytotoxic T lymphocytes (CTL). We believe that these atypical attributes make mshi an especially valuable model that may add significantly to our current understanding of how minor H loci may be structured and can modulate an immune response among MHC-matched individuals. We have recently identified a mshi-specific deletion in the Mtap7 gene (for microtubule- associated protein 7) that appears to be fully responsible for the male-sterility aspect of the mutant phenotype. Here we propose to use distinct skin-graft-exchange assays to explicitly determine whether mutant Mtap7 alleles (the Mtap7mshi deletion and Mtap7k.o., an engineered loss-of-function knock out mutation) can generate recessive, single-gene, antigen-loss barriers to graft compatibility in mice. While developing a congenic line that carries the Mtap7k.o. allele, we found a dominant, antigen-gain barrier to histocompatibility associated with the Mtap7k.o. mutation. We therefore propose to use another skin-graft-exchange assay to determine whether this dominant H-barrier is generated by the Mtap7k.o. mutation itself, or is instead the result of a gene (or genes) that flank the knock-out insertion. These short-term investigations are anticipated both to formally define mshi as a single- gene transplantation barrier and to provide new congenic mouse resources for Mtap7k.o. that will facilitate the future whole animal, in vitro cellular, and biochemical analysis of this novel and currently-underutilized H model. Importantly, these investigations will enhance undergraduate and master's-level research activity at CCSU by providing students with opportunities to learn the methods of immunogenetics, to collect and analyze data, and to make formal presentations of their results while they help to bring a unique histocompatibility model into the mainstream of functional and molecular analysis.